1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing roll film. More specifically, the invention relates to a film cassette that is capable of automatically advancing a non-protruding film leader to the exterior of the cassette shell responsive to unwinding rotation of a film spool within the shell.
2. Description of the Prior Art
In conventional 35 mm film manufacturers cassettes, such as manufactured by Eastman Kodak Co. and Fuji Photo Film Co. Ltd., the filmstrip is wound on a flanged spool which is rotatably supported within a cylindrical shell. A leading or forward-most portion of the filmstrip approximately 21/3 inches long, commonly referred to as a "film leader", normally protrudes from a light-trapped slit or mouth of the cassette shell. One end of the spool has a short axial extension which projects from the shell, enabling the spool to be turned by hand. If the spool is initially rotated in an unwinding direction, the film roll inside the shell will tend to expand radially since the inner end of the filmstrip is attached to the spool, and the fogged leader portion protruding from the slit will remain stationary. The film roll can expand radially until a non-slipping relation is established between its outermost convolution and the inner curved wall of the shell. Once this non-slipping relation exists, there is a binding effect between the film roll and the shell which prevents further rotation of the spool in the unwinding direction. Thus, rotation of the spool in the unwinding direction cannot serve to advance the filmstrip out of the shell, and it is necessary in the typical 35 mm camera to engage the protruding leader portion to draw the filmstrip out of the shell.
A 35 mm film cassette has been proposed which, unlike conventional film cassettes, can be operated to automatically advance a film leader out of the cassette shell by rotating the film spool in the unwinding direction. The film leader is normally non-protruding, i.e. it is located entirely within the cassette shell. Specifically, in U.S. Pat. No. 4,423,943, granted Jan. 3, 1984, there is disclosed a film cassette wherein the outermost convolution of the film roll wound on the film spool is radially constrained by respective circumferential lips of two axially spaced flanges of the spool to prevent the outermost convolution from contacting an inner curved wall of the cassette shell. The trailing end of the filmstrip is secured to the film spool, and the forward or leading end of the filmstrip is slightly tapered purportedly to allow it to freely extend from between the circumferential lips and rest against the shell wall. During initial unwinding rotation of the film spool, the leading end of the filmstrip is advanced to and through a non-lighttight film passageway in order to exit the cassette shell. As a result, all that is needed to advance the filmstrip out of the cassette shell is to rotate the film spool in the unwinding direction. However, according to U.S. Pat. No. 4,423,943, the film cassette is intended to be loaded in a camera only after the non-protruding leader is advanced out of the cassette shell. In the patent, it is suggested that one manually rotate the film spool relative to the cassette shell until the film leader can be manually grasped and attached to a film advancing device in the camera. Thus, the camera is not used to rotate the film spool to advance the film leader from the cassette shell.
More recently, in U.S. Pat. No. 4,834,306, granted May 30, 1989, U.S. Pat. No. 4,846,418, granted Jul. 11, 1989, U.S. Pat. No. 4,848,693, granted Jul. 18, 1989, U.S. Pat. No. 4,875,638, granted Oct. 24, 1989, U.S. Pat. No. 4,887,110, granted Dec. 12, 1989, and U.S. Pat. No. 4,894,673, granted Jan. 16, 1990, there are disclosed other film cassettes wherein a non-protruding leader is advanced automatically out of the cassette shell responsive to rotation of the film spool in an unwinding direction. In those patents, as compared to U.S. Pat. No. 4,423,943, however, there is no suggestion to manually rotate the film spool to expel the film leader. The film spool is rotated by a suitable drive mechanism in a camera.